Guitars typically have a body, a neck extending away from the body, and a peghead at the end of the neck. Strings are coupled under tension to pegs on the peghead, extend over a bridge that is mounted in the body, and are coupled at the bridge. In some guitars, the bridge is rigidly mounted in the body. In others, the bridge is mounted so that it is rotatable relative to the body. With a rotatable bridge, a player can rapidly change the tension, and therefore the pitch, of the strings to produce a tremulous, musical effect while playing. The player moves the bridge with a generally L-shaped bar that is mounted in the bridge. The rotatable bridge, the bar, and the other components for mounting the bridge are called a vibrato (such a device is also commonly known as a "tremolo").
Typical vibratos have two to five identical coil springs, each of which has one end rigidly connected to the bridge, and another end coupled to a bracket that is screwed into the body at a location between the bridge and the neck, i.e., the springs extend from the bridge toward the neck. These coil springs provide a tension that counteracts the tension of the strings.
When the guitar is not in use, the bridge is at a central or neutral position. In some guitars, from the neutral position, the bridge can be rotated relative to the body in either direction, and thus the bridge "floats." U.S. Pat. No. 4,638,711 discloses a bridge that can be selectively locked so that it is fixed, and unlocked so that it floats. A user locks and unlocks the bridge by rotating a control arm that is rigidly interconnected to a latch. The latch selectively interengages a catch mounted in the guitar body.
Some guitars have a bridge that can be moved in one direction relative to the neutral position, but not in the other. In some such guitars, a back portion of the bridge extends over and abuts an outside surface of the body in the neutral position. Consequently, the back of the bridge cannot move away further toward the body, but it can move away from the body. Therefore, the bar can be pushed toward the body to raise a back portion of the bridge, but cannot be pulled away from the body. This is referred to as a classic design.